In general, my invention relates to data processing systems. More particularly, it relates to apparatus for entering data words into a particular type of addressable memory, called a programmable read only memory (PROM), used in such data processing systems.
There are various type of addressable memories, some of which are classified as random access memories (RAMs) and others of which are classified as read only memories (ROMs). A ROM has utility in a wide range of data processing applications. Such devices have been used in many different types of instruction-controlled processors including special purpose sequencers and controllers and also including general purpose processors such as microprocessors. For many years, various semiconductor manufacturers have made and sold for use in such applications programmable read only memories (PROMs) that are programmed by means of a burn out technique. More recently, they have made and sold PROMs that are erasable. A representative example is a PROM made and sold by Texas Instruments Incorporated under the designation TMS 2716 JL. This particular PROM has 2048 locations each providing for the storage of an 8-bit data word, and is ultra-violet light erasable.
The various manufacturers of PROMs follow an industry-wide packaging convention, as they do for integrated circuits in general, to ensure both interchangeability and compatibility with standard sockets. Thus, a PROM supplied by any one of several manufacturers is contained in a standard dual-in-line package, most typically having 24 pins or terminals. One group of the terminals defines a set of address terminals. Another group of the terminals defines a set of data terminals. Another group of the terminals is provided so that operating power can be applied to the device. Finally, at least one of the terminals is used as a program control terminal. For a PROM that is programmable by means of the burn out technique, programming operation proceeds one bit at a time and a selected one of the data terminals is used as the program control terminal. For a PROM that is erasable, programming operation can proceed a data word at a time, and a terminal separate and apart from the data terminals is used as the program control terminal.
A need exists for a simple, easy to use, and inexpensive apparatus for high speed programming of such PROMs. Prior efforts directed toward this need have failed to provide reasonably satisfactory apparatus. Generally, the complexity involved in prior art PROM programmers, and the inevitable cost attending such complexity, makes them too expensive for many individuals and companies who want such programmers.
When I began to direct efforts toward this need, I did so with a view toward eliminating duplication of parts. I have reasoned that inasmuch as most, if not all, potential users of PROM programming apparatus already have in their possession equipment containing circuitry capable of performing a number of the various functions that are carried out by a PROM programming apparatus, it would be advantageous to tap such circuitry by providing an adapter to convert such existing equipment into a PROM programmer.
My invention, as is more fully developed below, not only taps such circuitry but also causes certain circuitry provided for implementing a reading function to play a role in a new function of entering data words into a PROM.